How does the tadpole even survive in him..
This is the question that gets overlooked the most. Why would a tadpole ever enter a dead body?
It's a magic tadpole which magic magic.
But Astarion doesn't seem all that dead, really. I'm not sure a tadpole could tell, as it was crawling in, that he was a vampire, and once inside it apparently goes into stasis, so it doesn't need to feed. Would Astarion become a vampiric mind flayer if he transformed? Who knows at this point?
